The invention relates to chainsaw guide bars and especially to liquid conducting channels in the guide bar. The invention also relates to a method of securing a tube in a guide bar.
It is well known to provide liquid channels in chainsaw guide bars to convey various liquids from the power unit of the chainsaw, such as lubricant for the nose sprocket, urea fungicide to tree stumps, or code marking paint to cut logs. If the guide bar is made from three thin plates welded together, the channels can be made as cut-outs in the middle plate, sealed by the outer plates and the welds, as described in U.S. Pat. Nos. 5,778,537 and No. 5,797,187.
If the channels have to be very pressure tight to avoid mixing of liquids from different channels, it is possible to use separate tubes located in the channels as disclosed in U.S. Pat. No. 5,845,402. One disadvantage with such tubes is that the cross-section available for the liquid is severely limited by the wall thickness of the tube having to be enclosed in a channel having the same thickness as the groove in the guide bar edge.
For guide bars made from one thick solid plate, another way of creating liquid channels has been proposed, where grooves are milled in a surface of the plate, and tubes are located in the grooves, held in place by brazing, soldering or glueing, as described in U.S. Pat. No. 5,050,303 and Swiss Patent 295 454. Since the groove depth is not restricted by the chain groove width, it is easier to use tubes with appropriate wall thickness without reducing the cross-section. The main disadvantage is that brazing or soldering results in heating the entire guide bar to a temperature which lowers its strength, and gluing is not reliable in severe winter cold. Relying on friction alone is not enough, since the bar and the tubes may be made from metals with different thermal expansion.
The present invention concerns a guide bar having an undercut channel and a tube disposed in the groove and held therein by an interference fit defined by the undercut. Thus, there is no need to employ brazing or soldering which could adversely affect the guide bar.
The invention also pertains to a method of securing the tube in the groove.